Benzoic acid is the simplest aromatic carboxylic acid on which so many of our wonderful polyphenols are based. It differs from the phenolic moiety we saw earlier today (click here) with the addition of that double bonded oxygen before the -OH. This means it becomes a carboxylic acid (which isn't that relevant at the moment unless you're an organic chemistry geek like me!).
Benzoic acid can inhibit the growth of mold , yeast, and some bacteria, is it regularly used as a preservative in food (anyone recognize sodium benzoate?) It is used as a treatment for fungal skin conditions.
It's found in various berries like raspberries, cranberries, pomegranate, and strawberries.
Hydroxybenzoic acids differ from benzoic acid by the inclusion of the -OH funcational group (you can see the addition at the bottom of this molecule, 4-hydroxybenzoic acid or 4-HBA). This family includes salicylic acid, protocatechuic acid, gallic acid, vanillic acid, and syringic acid. They are good anti-oxidants and fantastic anti-inflammatories, reducing redness and water retention as well.
We've learned gallic acid is a great wound and burn healer, as well as a good anti-oxidant and anti-inflammatory. Vanillic acid is a great anti-oxidant. Syringic acid is found mostly in red wine and whisky - not common ingredients in our products - and behaves as an anti-oxidant.
Salicylic acid is an interesting hydroxybenzoic acid. (You can see how it differs from a standard hydroxybenzoic acid - it has the -OH on the side instead of the bottom!) We know it from aspirin and acne medications as an anti-inflammatory and anti-acne medication, but how does it work? (I'll be doing a longer post on this topic shortly, but here's a summary). Salicylic acid induces exfoliation of our skin by reducing the adhesion between the cells so our skin can slough them off and expose new cells to the outside world. It enters our pores and removes the dirt, fatty acids, bacteria, and other things that might dwell within. It works from the top layers of our skin down, so it can lead to some sensitivity when the new skin is exposed. It can improve skin colour and texture, and remove ingrown hairs and debris from pores. (If you want to use this in your lotions in a powdered form, please read this post and the links on it for more information on safety.)
We find gallic acid in many of our ingredients - green tea, mango butter, pomegranate oil, and evening primrose oil - and we find salicylic acid in aloe vera and other extracts and hydrosols.
Cinnamon bark contains a lot of hydroxybenzoic acids in the form of protocatechuic acid (23 to 27 ppm), salicyclic acid (7 ppm), and syringic acid. Clove contains alot of gallic acid (175 ppm), with a bit of protocatechuic acid (10 ppm), genistic acid or 4-HBA (7 ppm), and syringic acid (8 ppm). Oats are chock full of hydroxybenzoic acids, which might explain why they are fantastic anti-inflammatory ingredients, whether in their full oaty form or hydrolyzed as a protein.